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A Ziad - One of the best experts on this subject based on the ideXlab platform.

  • monitoring daytime and nighttime optical turbulence profiles with the pml instrument
    AO4ELT6, 2019
    Co-Authors: E Aristidi, A Ziad, Yan Fanteicaujolle, Julien Chabe, Christophe Giordano, C Renaud, Henri Lanteri
    Abstract:

    The Profiler of Moon Limb is a recent instrument dedicated to the monitoring of optical turbulence profile of the atmosphere. Fluctuations of the Moon or the Sun limb allow to evaluate the index refraction structure constant C 2 n (h) and the wavefront coherence Outer Scale L 0 (h) as a function of the altitude h. The atmosphere is split into 33 layers with an altitude resolution varying from 100m (at the ground) to 2km (in the upper atmosphere). Profiles are obtained every 3mn during daytime and nighttime. We report last advances on the instrument and present some results obtained at the Plateau de Calern (France).

  • review of the Outer Scale of the atmospheric turbulence
    Proceedings of SPIE, 2016
    Co-Authors: A Ziad
    Abstract:

    Outer Scale is a relevant parameter for the experimental performance evaluation of large telescopes. Different techniques have been used for the Outer Scale estimation. In situ measurements with radiosounding balloons have given very small values of Outer Scale. This latter has also been estimated directly at the ground level from the wavefront analysis with High Angular Resolution (HAR) techniques using interferometric or Shack-Hartmann or more generally AO systems data. Dedicated instruments have been also developed for the Outer Scale monitoring such as the Generalized Seeing Monitor (GSM) and the Monitor of Outer Scale Profile (MOSP). The measured values of Outer Scale from HAR techniques, GSM and MOSP are somewhat coherent and are larger than the in situ results. The main explanation of this difference comes from the definition of the Outer Scale itself. This paper aims to give a review in a non-exhaustive way of different techniques and instruments for the measurement of the Outer Scale. Comparisons of Outer Scale measurements will be discussed in the light of the different definitions of this parameter, the associated observable quantities and the atmospheric turbulence model as well.

  • multi instrument measurement campaign at paranal in 2007 characterization of the Outer Scale and the seeing of the surface layer
    Astronomy and Astrophysics, 2010
    Co-Authors: Dali W Ali, A Ziad, J Maire, M Sarazin, J Borgnino, Amokrane Berdja, Gianluca Lombardi, Julio Navarrete, Vazquez H Ramio
    Abstract:

    Aims. Within the framework of site qualification for the future European large telescope E-ELT, a campaign of measurements was carried out for ten nights in December 2007 at Paranal using six independent instruments. Methods. To characterize the optical turbulence, two techniques were used: the statistical analysis of the fluctuations of the angle of arrival and the scintillation of the observed objects which are, in this case, a single star for DIMM, GSM, and MASS, a double star for Cute-SCIDAR, and Moon limb for MOSP and LuSci. Results. The optical parameters measured in this campaign and presented here are the seeing, the isoplanatic angle, the coherence time, and the Outer Scale. We obtain a good agreement with the value measured in previous campaigns. We also extracted the vertical profile of the turbulence given by C 2(h), and the profiles of the Outer Scale for the first time at Paranal. A comparison of the different results that we present here allows the determination of the energy distribution in the free atmosphere, on the ground layer as well as in the first meters above ground. This reveals a significant contribution of the surface layer to the degradation of the global seeing.

  • first statistics of the turbulence Outer Scale at dome c
    Astronomy and Astrophysics, 2008
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin, Eric Aristidi, E Fossat
    Abstract:

    Context. The Outer Scale of wavefronts is of interest for the dimensioning and the optimisation of the High Angular Resolution techniques such as Interferometry and Adaptive Optics, particularly for the new generation of telescopes such as the Extremely Large Telescopes (ELT). Aims. We aim to provide the first statistics of the Outer Scale at Dome C site in Antarctica to finalize the characterization of this site. Methods. A new version of the Generalized Seeing Monitor has been developed for extremely cold conditions. Two DIMMs (Differential Image Motion Monitor) were coupled to extract Angle-of-Arrival (AA) fluctuations using CCD detectors. Correlations of these AA fluctuations for different baselines lead to Outer Scale estimations. Results. For the first time, statistics of the Outer Scale at Dome C are provided leading to small values in the surface layer at Dome C. These small Outer Scale values compared to temperate sites considerably reduce the fringe excursion of interferometers and the low orders of the normalized amplitude of atmospheric Zernike coefficients, particularly the tip-tilt. Conclusions. The Dome C small Outer Scale combined with the large coherence time and large isoplanatic angle are very useful for the development of Adaptive Optics systems and long-baseline interferometers.

  • measurements of profiles of the wavefront Outer Scale using observations of the limb of the moon
    Monthly Notices of the Royal Astronomical Society, 2007
    Co-Authors: J Maire, A Ziad, J Borgnino, F Martin
    Abstract:

    The wavefront Outer Scale is an important parameter to use when evaluating the experimental performance of large aperture telescopes. Knowledge of three-dimensional atmospheric wavefront distortions is required for specifications of multiconjugate adaptive optics systems, which are essential for observations using Extremely Large Telescopes with a wider field of view. We aim to estimate the vertical distribution of the wavefront Outer Scale. We analyse the angular correlation of the fluctuations of the wavefront angle of arrival, deduced from image motion of the limb of the Moon. We use a simulated annealing algorithm to deduce the height dependence of the wavefront Outer Scale with given C 2 N profiles simultaneously measured with the scintillation detection and ranging (SCIDAR) instrument. We present results obtained during two campaigns of observation at the Mauna Kea Observatory (Hawaii) and the Observatoire de Haute Provence (France). Estimated profiles of the Outer Scale exhibit smaller values in the boundary layer than in the free atmosphere. Comparisons with measurements of the Outer Scale using the Generalized Seeing Monitor (GSM) are possible and give good agreement. We consider some implications for adaptive optics systems.

F Martin - One of the best experts on this subject based on the ideXlab platform.

  • first statistics of the turbulence Outer Scale at dome c
    Astronomy and Astrophysics, 2008
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin, Eric Aristidi, E Fossat
    Abstract:

    Context. The Outer Scale of wavefronts is of interest for the dimensioning and the optimisation of the High Angular Resolution techniques such as Interferometry and Adaptive Optics, particularly for the new generation of telescopes such as the Extremely Large Telescopes (ELT). Aims. We aim to provide the first statistics of the Outer Scale at Dome C site in Antarctica to finalize the characterization of this site. Methods. A new version of the Generalized Seeing Monitor has been developed for extremely cold conditions. Two DIMMs (Differential Image Motion Monitor) were coupled to extract Angle-of-Arrival (AA) fluctuations using CCD detectors. Correlations of these AA fluctuations for different baselines lead to Outer Scale estimations. Results. For the first time, statistics of the Outer Scale at Dome C are provided leading to small values in the surface layer at Dome C. These small Outer Scale values compared to temperate sites considerably reduce the fringe excursion of interferometers and the low orders of the normalized amplitude of atmospheric Zernike coefficients, particularly the tip-tilt. Conclusions. The Dome C small Outer Scale combined with the large coherence time and large isoplanatic angle are very useful for the development of Adaptive Optics systems and long-baseline interferometers.

  • measurements of profiles of the wavefront Outer Scale using observations of the limb of the moon
    Monthly Notices of the Royal Astronomical Society, 2007
    Co-Authors: J Maire, A Ziad, J Borgnino, F Martin
    Abstract:

    The wavefront Outer Scale is an important parameter to use when evaluating the experimental performance of large aperture telescopes. Knowledge of three-dimensional atmospheric wavefront distortions is required for specifications of multiconjugate adaptive optics systems, which are essential for observations using Extremely Large Telescopes with a wider field of view. We aim to estimate the vertical distribution of the wavefront Outer Scale. We analyse the angular correlation of the fluctuations of the wavefront angle of arrival, deduced from image motion of the limb of the Moon. We use a simulated annealing algorithm to deduce the height dependence of the wavefront Outer Scale with given C 2 N profiles simultaneously measured with the scintillation detection and ranging (SCIDAR) instrument. We present results obtained during two campaigns of observation at the Mauna Kea Observatory (Hawaii) and the Observatoire de Haute Provence (France). Estimated profiles of the Outer Scale exhibit smaller values in the boundary layer than in the free atmosphere. Comparisons with measurements of the Outer Scale using the Generalized Seeing Monitor (GSM) are possible and give good agreement. We consider some implications for adaptive optics systems.

  • wavefront Outer Scale deduced from interferometric dispersed fringes
    Astronomy and Astrophysics, 2006
    Co-Authors: J Maire, A Ziad, J Borgnino, F Martin, D Mourard, S Jankov, D Bonneau, F Patru
    Abstract:

    In addition to site characterization, measurements of critical atmospheric parameters are required to design and to optimize future adaptive optic systems and long-baseline interferometers. It is possible to estimate seeing conditions by processing data obtained with existing High Angular Resolution instruments. We report the results of joint observations with the GI2T interferometer and the GSM site-testing monitor performed over a period of several nights. We compared estimates of the wavefront Outer Scale done at various baselines as well as the seeing (Fried’s parameter). We processed interferometric data by calculating power spectra of dispersed fringe images. Deduced measurements of the optical path difference lead to the estimates of the Outer Scale. We found that the Outer Scale values obtained from the GI2T data are mostly in the 5−30 m range, in good agreement with GSM measurements.

  • optical parameters relevant for high angular resolution at paranal from gsm instrument and surface layer contribution
    Astronomy & Astrophysics Supplement Series, 2000
    Co-Authors: F Martin, A Ziad, A Agabi, Andrei Tokovinin, J Borgnino, Rodolphe Conan, H Trinquet, M Sarazin
    Abstract:

    Main atmospheric parameters characterizing the turbulence were measured at the Paranal ESO Observatory (Chile) with the Generalized Seeing Monitor (GSM) during 19 nights in November{December 1998. The median seeing for this period was 0:88 00 , a little worse than average, the spatial coherence Outer Scale of the wavefrontL0 =2 2:0 m and the median isoplanatic angle 0 =1 :90 00 . A very good agreement with seeing values given by ESO DIMM was found. Eects of ground layer turbulence were estimated from measurements of temperature micro{fluctuations at several altitudes. These measurements revealed that the rst 21 m above ground account for 12.5% of the total turbulent energy. Comparison between GSM and ESO DIMM values have permitted to highlight a local phenomenon which occurs sometimes at the site in the middle of the night. Statistics of the refractive index structure constant C 2 n in the surface layer is also studied.

  • optimized spectral bandwidth in high angular resolution imaging effect of a finite spatial coherence Outer Scale
    Experimental Astronomy, 1994
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin
    Abstract:

    In the case of high angular resolution techniques (speckle interferometry, long baseline Michelson interferometry), one has studied how varies the signal-to-noise ratio (SNR) in terms of the spectral bandwidth Δλ. For values of Δλ varying from 0 up to 100 nanometers, it is shown that the SNR, contrary to the predictions, has no maximum value. In addition, in the case of the high frequency approximation, the effects of a finite spatial-coherence Outer Scale, the influence of the turbulence model used and of the “optical energy” of the turbulence on the optimal spectral bandwidth have been analyzed and discussed.

A Agabi - One of the best experts on this subject based on the ideXlab platform.

  • first statistics of the turbulence Outer Scale at dome c
    Astronomy and Astrophysics, 2008
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin, Eric Aristidi, E Fossat
    Abstract:

    Context. The Outer Scale of wavefronts is of interest for the dimensioning and the optimisation of the High Angular Resolution techniques such as Interferometry and Adaptive Optics, particularly for the new generation of telescopes such as the Extremely Large Telescopes (ELT). Aims. We aim to provide the first statistics of the Outer Scale at Dome C site in Antarctica to finalize the characterization of this site. Methods. A new version of the Generalized Seeing Monitor has been developed for extremely cold conditions. Two DIMMs (Differential Image Motion Monitor) were coupled to extract Angle-of-Arrival (AA) fluctuations using CCD detectors. Correlations of these AA fluctuations for different baselines lead to Outer Scale estimations. Results. For the first time, statistics of the Outer Scale at Dome C are provided leading to small values in the surface layer at Dome C. These small Outer Scale values compared to temperate sites considerably reduce the fringe excursion of interferometers and the low orders of the normalized amplitude of atmospheric Zernike coefficients, particularly the tip-tilt. Conclusions. The Dome C small Outer Scale combined with the large coherence time and large isoplanatic angle are very useful for the development of Adaptive Optics systems and long-baseline interferometers.

  • Seeing, Outer Scale of optical turbulence, and coherence Outer Scale at different astronomical sites using instruments on meteorological balloons
    Astronomy and Astrophysics, 2004
    Co-Authors: A. Abahamid, Jean Vernin, Zouhair Benkhaldoun, A. Jabiri, M. Azouit, A Agabi
    Abstract:

    Here we analyze 168 optical turbulence profiles made at nine different locations worldwide by means of free flight balloons equipped with instrumentation. Seeing eFWHM, optical turbulence Outer Scales Lo, and wavefront Outer Scales £o are derived for the different locations and taking into account the contribution of the surface layer (0, 50 m), the boundary layer (0, 1 km) and the free atmosphere (1 km, 30 km). Noticeable changes are found between the different locations, mainly due to the boundary layer contribution as well as the surface layer contribution. The free atmosphere contribution seems almost the same for each site. There is a very good coherence between the Outer Scale derived by us and that measured using the Generalized Seeing Monitor (GSM) technique.

  • optical parameters relevant for high angular resolution at paranal from gsm instrument and surface layer contribution
    Astronomy & Astrophysics Supplement Series, 2000
    Co-Authors: F Martin, A Ziad, A Agabi, Andrei Tokovinin, J Borgnino, Rodolphe Conan, H Trinquet, M Sarazin
    Abstract:

    Main atmospheric parameters characterizing the turbulence were measured at the Paranal ESO Observatory (Chile) with the Generalized Seeing Monitor (GSM) during 19 nights in November{December 1998. The median seeing for this period was 0:88 00 , a little worse than average, the spatial coherence Outer Scale of the wavefrontL0 =2 2:0 m and the median isoplanatic angle 0 =1 :90 00 . A very good agreement with seeing values given by ESO DIMM was found. Eects of ground layer turbulence were estimated from measurements of temperature micro{fluctuations at several altitudes. These measurements revealed that the rst 21 m above ground account for 12.5% of the total turbulent energy. Comparison between GSM and ESO DIMM values have permitted to highlight a local phenomenon which occurs sometimes at the site in the middle of the night. Statistics of the refractive index structure constant C 2 n in the surface layer is also studied.

  • optimized spectral bandwidth in high angular resolution imaging effect of a finite spatial coherence Outer Scale
    Experimental Astronomy, 1994
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin
    Abstract:

    In the case of high angular resolution techniques (speckle interferometry, long baseline Michelson interferometry), one has studied how varies the signal-to-noise ratio (SNR) in terms of the spectral bandwidth Δλ. For values of Δλ varying from 0 up to 100 nanometers, it is shown that the SNR, contrary to the predictions, has no maximum value. In addition, in the case of the high frequency approximation, the effects of a finite spatial-coherence Outer Scale, the influence of the turbulence model used and of the “optical energy” of the turbulence on the optimal spectral bandwidth have been analyzed and discussed.

  • experimental estimation of the spatial coherence Outer Scale from a wavefront statistical analysis
    Astronomy and Astrophysics, 1994
    Co-Authors: A Ziad, F Martin, J Borgnino, A Agabi
    Abstract:

    Estimations of the spatial-coherence Outer Scale L 0 relevant for high angular resolution imaging are deduced from measurements of both angle-of-arrival normalized covariance and difference of the variances measured with two different size circular apertures. These measurements have been obtained by means of an experimental device identical to a differential image motion monitor. Simultaneous estimations of Fried's parameter r 0 are obtained from this difference and compared to those deduced from the structure function (ESO's DIMM method). The sensitivity of these techniques to the different noises as well as to the model describing atmospheric turbulence, is deeply analyzed and discussed

Stanislav N. Gorb - One of the best experts on this subject based on the ideXlab platform.

  • material properties of the skin of the kenyan sand boa gongylophis colubrinus squamata boidae
    Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2010
    Co-Authors: Mariechristin G Klein, Julia Deuschle, Stanislav N. Gorb
    Abstract:

    On the basis of structural data, it has been previously assumed that the integument of snakes consists of a hard, robust, inflexible Outer surface (Oberhautchen and β-layer) and soft, flexible inner layers (α-layers). The aim of this study was to compare material properties of the Outer and inner Scale layers of the exuvium of Gongylophis colubrinus, to relate the structure of the snake integument to its mechanical properties. The nanoindentation experiments have demonstrated that the Outer Scale layers are harder, and have a higher effective elastic modulus than the inner Scale layers. The results obtained provide strong evidence about the presence of a gradient in the material properties of the snake integument. The possible functional significance of this gradient is discussed here as a feature minimizing damage to the integument during sliding locomotion on an abrasive surface, such as sand.

  • Material properties of the skin of the Kenyan sand boa Gongylophis colubrinus (Squamata, Boidae)
    Journal of comparative physiology. A Neuroethology sensory neural and behavioral physiology, 2010
    Co-Authors: Mariechristin G Klein, Julia Deuschle, Stanislav N. Gorb
    Abstract:

    On the basis of structural data, it has been previously assumed that the integument of snakes consists of a hard, robust, inflexible Outer surface (Oberhautchen and beta-layer) and soft, flexible inner layers (alpha-layers). The aim of this study was to compare material properties of the Outer and inner Scale layers of the exuvium of Gongylophis colubrinus, to relate the structure of the snake integument to its mechanical properties. The nanoindentation experiments have demonstrated that the Outer Scale layers are harder, and have a higher effective elastic modulus than the inner Scale layers. The results obtained provide strong evidence about the presence of a gradient in the material properties of the snake integument. The possible functional significance of this gradient is discussed here as a feature minimizing damage to the integument during sliding locomotion on an abrasive surface, such as sand.

J Borgnino - One of the best experts on this subject based on the ideXlab platform.

  • first statistics of the turbulence Outer Scale at dome c
    Astronomy and Astrophysics, 2008
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin, Eric Aristidi, E Fossat
    Abstract:

    Context. The Outer Scale of wavefronts is of interest for the dimensioning and the optimisation of the High Angular Resolution techniques such as Interferometry and Adaptive Optics, particularly for the new generation of telescopes such as the Extremely Large Telescopes (ELT). Aims. We aim to provide the first statistics of the Outer Scale at Dome C site in Antarctica to finalize the characterization of this site. Methods. A new version of the Generalized Seeing Monitor has been developed for extremely cold conditions. Two DIMMs (Differential Image Motion Monitor) were coupled to extract Angle-of-Arrival (AA) fluctuations using CCD detectors. Correlations of these AA fluctuations for different baselines lead to Outer Scale estimations. Results. For the first time, statistics of the Outer Scale at Dome C are provided leading to small values in the surface layer at Dome C. These small Outer Scale values compared to temperate sites considerably reduce the fringe excursion of interferometers and the low orders of the normalized amplitude of atmospheric Zernike coefficients, particularly the tip-tilt. Conclusions. The Dome C small Outer Scale combined with the large coherence time and large isoplanatic angle are very useful for the development of Adaptive Optics systems and long-baseline interferometers.

  • measurements of profiles of the wavefront Outer Scale using observations of the limb of the moon
    Monthly Notices of the Royal Astronomical Society, 2007
    Co-Authors: J Maire, A Ziad, J Borgnino, F Martin
    Abstract:

    The wavefront Outer Scale is an important parameter to use when evaluating the experimental performance of large aperture telescopes. Knowledge of three-dimensional atmospheric wavefront distortions is required for specifications of multiconjugate adaptive optics systems, which are essential for observations using Extremely Large Telescopes with a wider field of view. We aim to estimate the vertical distribution of the wavefront Outer Scale. We analyse the angular correlation of the fluctuations of the wavefront angle of arrival, deduced from image motion of the limb of the Moon. We use a simulated annealing algorithm to deduce the height dependence of the wavefront Outer Scale with given C 2 N profiles simultaneously measured with the scintillation detection and ranging (SCIDAR) instrument. We present results obtained during two campaigns of observation at the Mauna Kea Observatory (Hawaii) and the Observatoire de Haute Provence (France). Estimated profiles of the Outer Scale exhibit smaller values in the boundary layer than in the free atmosphere. Comparisons with measurements of the Outer Scale using the Generalized Seeing Monitor (GSM) are possible and give good agreement. We consider some implications for adaptive optics systems.

  • wavefront Outer Scale deduced from interferometric dispersed fringes
    Astronomy and Astrophysics, 2006
    Co-Authors: J Maire, A Ziad, J Borgnino, F Martin, D Mourard, S Jankov, D Bonneau, F Patru
    Abstract:

    In addition to site characterization, measurements of critical atmospheric parameters are required to design and to optimize future adaptive optic systems and long-baseline interferometers. It is possible to estimate seeing conditions by processing data obtained with existing High Angular Resolution instruments. We report the results of joint observations with the GI2T interferometer and the GSM site-testing monitor performed over a period of several nights. We compared estimates of the wavefront Outer Scale done at various baselines as well as the seeing (Fried’s parameter). We processed interferometric data by calculating power spectra of dispersed fringe images. Deduced measurements of the optical path difference lead to the estimates of the Outer Scale. We found that the Outer Scale values obtained from the GI2T data are mostly in the 5−30 m range, in good agreement with GSM measurements.

  • comparison of measurements of the Outer Scale of turbulence by three different techniques
    Applied Optics, 2004
    Co-Authors: A Ziad, J Borgnino, Matthias Schock, Gary Chanan, Mitchell Troy, Richard Dekany, Benjamin F Lane, Francois Martin
    Abstract:

    We have made simultaneous and nearly simultaneous measurements of L0, the Outer Scale of turbulence, at the Palomar Observatory by using three techniques: angle-of-arrival covariance measurements with the Generalized Seeing Monitor (GSM), differential-image-motion measurements with the adaptive-optics system on the Hale 5-m telescope, and fringe speed measurements with the Palomar Testbed Interferometer (PTI). The three techniques give consistent results, an Outer Scale of approximately 10-20 m, despite the fact that the spatial Scales of the three instruments vary from 1 m for the GSM to 100 m for the PTI.

  • optimized spectral bandwidth in high angular resolution imaging effect of a finite spatial coherence Outer Scale
    Experimental Astronomy, 1994
    Co-Authors: A Ziad, J Borgnino, A Agabi, F Martin
    Abstract:

    In the case of high angular resolution techniques (speckle interferometry, long baseline Michelson interferometry), one has studied how varies the signal-to-noise ratio (SNR) in terms of the spectral bandwidth Δλ. For values of Δλ varying from 0 up to 100 nanometers, it is shown that the SNR, contrary to the predictions, has no maximum value. In addition, in the case of the high frequency approximation, the effects of a finite spatial-coherence Outer Scale, the influence of the turbulence model used and of the “optical energy” of the turbulence on the optimal spectral bandwidth have been analyzed and discussed.